1. Field of the Invention
The present invention pertains to an object positioning device, and in particular, to a three-dimensional positioning device and a positioning method that are used for measuring instruments and are of high accuracy in terms of ideal positioning and low cost.
2. Discussion of the Background Art
There are many opportunities for positioning probes for transmitting and receiving electric signals in cases of circuits to be tested and for heads for recording data or reading data from recording media, etc., with measuring instruments. Furthermore, in recent years there has been a demand for miniature, high-density circuits and recording media, and as a result, higher positioning accuracy. In order to facilitate understanding of the present invention, the latter will be described below in the present Specification using as an example magnetic recording media, particularly, the testing device for magnetic heads that read-write data onto a hard disk. The device and method that will be explained belong to the ideal field of use of the present invention, but the field of use of the present invention is not restricted to that described herein.
The magnetic head positioning device simulates the actual read-write operation of a magnetic head and therefore, has movable carriages with which approximate positioning is performed and a precision positioning stage with which precision positioning is performed. The stage for precision positioning, onto which a magnetic head is loaded and this magnetic head is driven and positioned by a piezo element, is anchored on a movable carriages and operates as one unit with the movable carriage. Although the accuracy of the approximate positioning is inferior to the accuracy of the precision positioning, its stability must be high enough to guarantee the accuracy that is realized with the precision positioning. The positioning range of the stage for precision positioning is 10 xcexcm and resolution is from several nm to several ten nm, and the movable carriage has a range of movement from 100 mm to 150 mm, in typical positioning devices. Unless otherwise described in the Specification of the present invention, the magnetic head and precision positioning stage and related circuits, etc., are referred to simply as xe2x80x9cheadxe2x80x9d.
It is necessary, for instance, to perform positioning in a horizontal direction and positioning in a vertical direction in order to produce a more exact approximate positioning of the head. Therefore, a stationary plate that provides a reference horizontal surface or a mechanism equivalent to this stationary plate, etc., is set up and the head is positioned at a predetermined position on this reference horizontal surface and at a predetermined height from this reference horizontal surface.
Positioning device 10 of a first prior art design is shown in FIG. 1. By means of positioning device 10, a pair of linear guides 12A and B, which are set up parallel to one another on stationary plate 11, guide movable carriage 13 traveling along these linear guides 12A and B. Head 16 is anchored to movable carriage 13. Servo motor 15 is anchored to one end of linear guides 12A and B and the axis of this servo motor 15 engages and drives nut 17, which is attached to movable carriage 13 via ball screw 14, to drive movable carriage 13. Ball screw 14 is turned when the axis of servo motor 15 rotates and movable carriage 13 moves forward or backward along linear guides 12A and B. Movable carriage 13 moves back to the side of servo motor 15 and head 16 is replaced, adjusted, etc. Then movable carriage 13 is moved forward away from the side of servo motor 15 and is stopped at a predetermined position, where the head is tested, etc. The height of linear guides 12A and B and movable carriage 13 is selected so that the height of head 16 from the surface of the stationary plate is a predetermined height.
Positioning device 20 of a second prior art design is shown in FIG. 2. By means of positioning device 20, tilt base 24 is attached so that it can turn as needed to tilt axis of rotation 23 anchored to a pair of bearings 22A and B set up parallel to one another on stationary plate 21. Tilt base 24 holds pedestal 25, to which head 26 is anchored at the end opposite tilt axis of rotation 23, and performs a tilt operation (inclination operation) in the direction of arrow T in the figure in order to position head 26 using an actuator, such as an air cylinder, etc., that is not shown. Head 26 is positioned away from stationary plate 21 by the actuator and the head is replaced, adjusted, etc., then tilt base 24 is lowered toward stationary plate 21 and re-positioned by the actuator, and tests, etc., are performed on head 26 and the media.
In the above-mentioned example, tilt axis of rotation 23 was parallel to the top surface of stationary plate 21, but a structure wherein it is perpendicular is also possible. In this case, tilt base 24 engages with and is driven by tilt axis of rotation 23 and the head is moved up and down parallel with the top surface of stationary plate 21.
Positioning device 30 of a third prior art design is shown in FIG. 3. By means of positioning device 30, movable carriage 34 moves along a pair of guides 32A and B set up parallel to one another on stationary plate 31. The stators of linear motor 36 are attached to guide 32B and movable carriage 34 functions as a runner of linear motor 36. Moreover, linear scale 37 is attached to guide 32A along the direction in which the movable carriage moves and gives the position of movable carriage 34.
In addition, by means of the technology disclosed in International Patent Application WO 99/66498 (Dec. 23, 1999) in which the above-mentioned design was modified, movable carriage 34 in FIG. 3 is moved by being floated up from around the outside by air bearings. On the other hand, movable carriage 34 is firmly vacuum suctioned onto stationary plate 31 when it stops so that it is positioned with stability. Movable carriage 34 is pre-vacuum suctioned at the vacuum suction opening and when running, is floated up by the compressed air that is introduced from the air release hole. This technological solution is very stable with high-speed designs, reaching a stability of xc2x110 nm within 50 ms after the carriage moves.
The positioning devices of the above-mentioned first and second designs of the prior art are relatively inexpensive. However, the accuracy and stability of the resting position of moving tubes and the accuracy and stability of the posture of the movable carriages are insufficient. The movable carriages are held by ball screws and axes of rotation, both when driven and when resting, and therefore, the accuracy and stability of the base position are poor because of restrictions in terms of backlash and rigidity of the ball screws, the rigidity of the axis of rotation, and the holding power of the servo motor and actuator. When viewed in terms of resting convergence speed, the vibration amplitude increases as rigidity decreases and speed is relatively slow. Moreover, it is difficult to always keep the suctioning surface and anchoring surface (top surface of the stationary plate) for the movable carriages parallel to one another and therefore, efficient vacuum suctioning for stable anchoring of the resting carriage position is not possible.
By means of the positioning device of the above-mentioned third design of the prior art, the connection with the drive mechanism is cut when the moving carriage is resting and the position is maintained with stability by vacuum suctioning. However, there is a demand for a very high finishing accuracy of the compressed-air release opening and flotation surface in order to produce stable flotation in particular. Therefore, the finishing cost of the movable carriage increases. Moreover, because the amount by which the movable carriage floats has a strong effect on positioning accuracy, it is necessary to accurately adjust the amount of flotation. Consequently, device cost increases.
Therefore, there is a strong need for the presentation of a very stable, inexpensive positioning device that has both the low cost of the positioning devices of the above-mentioned first and second designs of the prior art, etc., and the high stability of the positioning device of the above-mentioned third design of the prior art, etc.
By means of the positioning device of the present invention, the connection between first and second movable carriages is broken and they are moved away from one another to eliminate the mechanical vibrations and force originating from the second movable carriage so that when the first movable carriage is positioned and comes to a rest, position stability is improved, using inexpensive structural elements and structural method.
The positioning device for determining the position of an object that is the first subject of the present invention comprises an anchoring surface, a first movable carriage on which this object is loaded and which has a means for suctioning onto this anchoring surface, a second movable carriage which has a drive assembly and which is connected with the first movable carriage as needed, and a connecting means which controls said connection of said first and second movable carriages. Moreover, said first and second movable carriages are connected by the above-mentioned drive assembly and said first movable carriage is conveyed to a predetermined position on the above-mentioned anchoring surface and said first movable carriage is suctioned and anchored onto said anchoring surface at this predetermined position by a means for breaking the connection between said first and second movable carriages and performing the above-mentioned suctioning so that the above-mentioned object is positioned.
By means of a positioning device with this type of structure, an inexpensive drive assembly and the second movable carriage can be connected to or disconnected from the first movable carriage with an inexpensive connecting means. Consequently, an inexpensive drive assembly and inexpensive second movable carriage can be used with which propagation of mechanical noise to the object is minimized and high positioning stability is maintained. Therefore, the cost of the positioning device is reduced.
Moreover, the connecting means is anchored to said first movable carriage and the connecting means can therefore also use the power that is employed for suctioning by the suctioning device. That is, the device can be simplified by common use of object control and consumed power. Moreover, it is also possible to select the method of controlling the connecting means as needed so that the connecting means is anchored to the above-mentioned second movable carriage and the connecting means is unaffected by the first movable carriage once the first movable carriage has been suctioned and anchored.
Furthermore, by using a vacuum suction plate with a gas feed and evacuation opening that communicates with a gas feed and evaluation device as the means for performing suctioning, the device, which uses inexpensive, ordinary air, is inexpensive and easy to maintain, and operating cost is also low.
Selecting a structure with a ball screw which engages with this first movable carriage and which is used for moving the above-mentioned first movable carriage forward and a motor which is used for turning this ball screw as the above-mentioned drive assembly is ideal for linearly moving an object back and forth between the test position and the holding position with an ordinary, inexpensive device.
At the same time, it is also possible to use a structure that has an axis of rotation which keeps the above-mentioned first movable carriage inclined as needed with respect to the above-mentioned anchoring surface and which is used for inclining the above-mentioned first movable carriage with respect to the above-mentioned stationary surface, and an actuator which controls the inclination of the first movable carriage by rotating this axis of rotation as the drive assembly. This is ideal for moving an object between the test position and the holding position along an almost constant floor surface area with an inexpensive device. Moreover, the connecting means is also simple.
Furthermore, although a different embodiment, it is possible to use a structure wherein the drive assembly has a perpendicular axis of rotation anchored to this first movable carriage and perpendicular to the above-mentioned anchoring surface which is used for turning and moving said first movable carriage along the above-mentioned anchoring surface, and a motor for rotating this perpendicular axis of rotation. This is ideal for moving an object to the left and right between the test position and the holding position using an ordinary inexpensive device.
In addition, it is also possible to use a drive assembly that moves said first movable carriage along the direction perpendicular to the above-mentioned anchoring surface. In this case, the structure is ideal wherein the drive assembly is a rotary actuator with a cam and the above-mentioned first movable carriage has a linear slider with a cam follower that engages with said cam.
The method for holding an object at a predetermined position on an anchoring surface at a predetermined height from this anchoring surface, which is the second subject of the present invention, comprises the step whereby a first movable carriage with a means for suctioning onto the above-mentioned anchoring surface is made ready, the step whereby the above-mentioned object is loaded onto said first movable carriage, the step whereby a second movable carriage with a drive assembly and which can be freely connected with the first movable carriage is made ready, the step whereby the above-mentioned connecting means for said first and second movable carriages is made ready, the step whereby said first and second movable carriages are connected by the above-mentioned drive assembly and said first movable carriage is conveyed to a predetermined position on the above-mentioned anchoring surface, and the step whereby said first movable carriage is suctioned and anchored onto the above-mentioned anchoring surface at the above-mentioned predetermined position by a means that breaks the connection between said first and second movable carriages and performs the above-mentioned suctioning. Moreover, it is preferred that said suctioning be started before the connection between said first and second movable carriages is broken in the above-mentioned suctioning and anchoring step because positioning can be accomplished with greater accuracy. It is clear that the same results as with the first subject are obtained with this second subject of the invention of the present invention.